1. Field of the Invention
The present invention relates to a sensor and memory unit and more specifically to a catheter sensor and memory unit for monitoring a chemical, physical, or biological parameter and for providing a standard output. The unit includes a non-uniform sensor in a catheter and a memory connected thereto and, containing-correction information which is supplied in parallel with the sensor output to signal conditioning and processing circuits to produce a standard output for the parameter(s) sensed.
2. Description of the Prior Art
Sensors or sensor combinations that provide an electrically processable output signal are used in many fields for measuring and/or detecting a variety of phenomena. These phenomena may, for example, be of a chemical, physical or biological nature. As used herein, the term sensor can include a combination of co-operating sensors.
In the mass manufacture of sensors, an almost unavoidable problem is encountered in that, from one specimen sensor to another, the sensors have slightly different properties and exhibit a different behavior. This renders it difficult to compare accurately the results of measurements made with different sensors.
This drawback has been overcome in some instances by either applying very high standards in the production of the sensors, carrying out a very strict selection after production, and/or calibrating each sensor before use. These methods are time consuming, either on the side of production or on that of the consumer, and expensive.
An user of a sensor who is aware of the problem of the different response characteristics of different sensors will try to use the same sensor all the time after it has been calibrated. This, however, is often impossible in the field of medical sensors since certain sensors can only be used once and/or have to be replaced after several uses thereof to avoid infection to a patient which can occur if a sensor is sterilized more than a few times.
Also, heretofore, a sensor which can be easily calibrated before use has not been readily available.
Furthermore, the response characteristics of one and the same sensor may vary in time, as a result of inherent aging effects and/or as a result of its exposure to ambient conditions, such as temperature and pressure.
Heretofore attempts have been made to developed an "ideal" sensor in order to eliminate the above drawbacks. However, it is practically impossible to produce an "ideal" or perfect sensor and this is especially so in the case of sensors which must be mass produced in large numbers.
Additionally, it has been proposed to provide each sensor with an identification plate, chained, for example, to the sensor, and showing some characteristics of the sensor. The user can then correct the sensor's output signals by means of the data on the identification plate. Such correction may be effected, for example, by adjusting an electrical circuit arrangement which processes the sensor signals. This can be done, for example, by adjusting a potentiometer or thumb-wheel switches to effect the desired correction in the electrical circuit. This method is used, for example, in Fleisch Flow Transducers.
However, this method is not always effective since errors may occur in correlating a plate with a sensor, both during production, because, for example, the identification plates may be interchanged, and in use, because an identification plate is misread or the electrical circuit is maladjusted.
Such interchange of identification plates is not an uncommon event and periodically occurs in the mass production of sensors.
Furthermore, the adjustment of an electrical circuit by hand is a cumbersome job and lowers the market appeal of such sensors provided with identification plates.
In some sensor applications, such as, for example in the medical field, it is of great importance that the risk of error be as low as possible. As a result, manual adjustment of equipment coupled to sensors on the basis of data on an identification plate is highly undesirable.
Furthermore, even if manufacturing techniques are perfected to such an extent that certain types of sensors can be made sufficiently "ideal", it is yet often desirable to record specific unique information associated with a particular sensor in such a manner that when the sensor is used such unique information is immediately available without the risk of errors.
Such unique information may comprise, for example, the type of sensor, or type number, serial number, date of production, or safe use life of the sensor.
Consequently, an identification plate sensor combination as described above although useable in the medical field, still has the inherent drawbacks described above.
Still further it has been proposed in U.K. patent application No. 2,065,890 for: SENSOR SYSTEM WITH NON-LINEARITY CORRECTION by Felix J. Houvig, published July 1, 1981 to provide a sensor system comprising a fluid tight housing having a fluid pressure inlet portion and the sensor is mounted to an electronic component housing for electronic circuitry including sensor amplifying circuits, a power supply, a transistor switch, a shift register and a PROM. A signal isolation interface circuit is fixed to one side of the electronic component housing for connecting the electronic component housing and electronic circuitry therein to a microprocessor.
The PROM in this sensor system is programmed with correction control data to compensate for non-linearity and/or, perhaps, other characteristics in the sensor output.
As will be described in greater detail hereinafter, the sensor and memory unit of the present invention differ from the sensors or sensor systems described above by providing an integral, unitary sensor and memory combination unit where information regarding the characteristics of the sensor or sensor-memory combination are permanently recorded in the memory and the sensor and memory are indissolubly coupled together. The recorded information can be automatically and directly read and retrieved by separate electronic processing circuitry.
Also the sensor and memory unit of the present invention preferably includes a catheter for carrying the sensor therein, such as at one end thereof, and for providing a conduit for wire conductor connections between the sensor or sensors in the catheter and the memory fixed to the catheter. Such sensor and memory unit is particularly adapted for use in the medical field.
More specifically with respect to the sensor system disclosed in U.K patent application No. 2,065,890 such sensor system decribes a method for correcting an output signal of an electronic signal conditioning circuit where memory information may be used for non-ideal transducer characteristics, such as non-linearity, which is reflected in the output signal of the electronic signal conditioning circuit. However, an ideal linear transducer may have sensitivity deviation from nominal sensitivity specifications and the U.K. patent application No. 2,065,890 does not indicate how these differences in sensitivity from nominal specification can be treated.
As described in further detail hereinafter the sensor and memory unit of the present invention are utilized in a system where an ideal transducer is assumed, i.e., a perfectly linear transducer. However, all sensors built deviate from the nominal specification established therefor. In the memory of the present invention the actual specification of the ideal transducer (for example, pressure sensitivity, offset, temperature sensitivity) are stored.
In a sensor system including signal processing and conditioning circuitry that can be coupled to the sensor and memory unit of the present invention, the information data stored in the memory is decoded and the characteristics of the signal conditioning circuitry associated with the microprocessor are changed (for example, the amplification factor or offset are changed). As a result, the output signal from the signal conditioning circuitry always will be the same as for a sensor or transducer with nominal specification for any sensor and memory unit of the present invention that is coupled into the sensor system. Stated otherwise, the final output signal is standard for every transducer whereas in the sensor system disclosed in U.K. patent application No. 2,065,890, the amplitude of the signal depends on transducer sensitivity.
Also the memory can contain direct data for the adjustment of the signal processing and conditioning circuitry instead of data concerning the sensor characteristics.
Finally, and what has been explained above, the sensor and memory unit of the present invention is just that, namely a sensor and memory unit alone without any signal processing and conditioning circuitry, so as to provide a simple and single, compact unit which can be incorporated into a catheter for use in the medical field and which can be detachably coupled to any one of several types of signal processing and conditioning circuits.